Induction-furnace protective circuits



April 2l,A 1931. J. BREISKY ET AL l 1,801,791

INDUCTIN FURNACE PROTECTIVE CIRCUITS Filed March 5, 1950 `unimore MBreisy ThogYzas H. Long 2p 26 ATTORNEY rammed Apr. 21, 1931 UNITEDSTATES PATENT OFFICE JOHN V. BREISKY, OF PITTSIBURGH, AND THOMAS E.LONG, F IRWIN, PENNSYLVANIA,

ASSIGNORS T0 WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A COB-PORATION OF PENNSYLVANIA' INDUCTION-FUBNACE PROTECTIVE CIRCUITSApplication filed March 5,

Our invention relates to electric furnaces and more particularly toelectric induction furnaces. Y l

'An object 'of our invention is to provide a means for and a method ofprotecting the inductor coil against engagement by material lescapingfrom a crucible located within it.

Another object of our invention'is to provide a control systemcooperating with the inductor coil that shall preclude energizationthereof in case a dangerous breakdown occurs in the insulation in thefurnace structure.

In practicing our invention, we provide a two-part shield, preferablymade of nonmagnetic but electric-conducting material, located in thespace between a crucible and a surroundin inductor coil, the two partsof the shield ge each other as well as from the coil and the crucible.We provide, also, a source of electric energy for the two-part shieldand means operatively associated with the inductor coil and the circuitconnected to the two-part shield for interrupting the supply of electricenergy to the coil in case of the existence of an electric circuitbetween the two parts of the shield.

In the single sheet of drawings:

Figure 1 is a view, in horizontal section,

3Q of a part of an induction-furnace structure embodying our invention,taken on the line I-I of Fig. 2.

Fig. 2 is a view, in vertical section, through a furnace structureembodying our invention,

certain portions being broken away to show the internal assemblythereof. Fig. 3 is a schematic top plan View of a modified form oftwo-part shleld, and;

Fig'. 4 is a View, in vertical section, taken on the line IV--IV of Fig.3.

We have found, in the operation of induction furnaces, particularly whenmelting certain metals or alloys that there is a possibility ofthecrucible cracking in places. The

cracks or openings are so small as to be more ing electrically insulatedfrom 1930. Serial N0. 433,292.

properly called hair cracks but areof suffi-- v engagement with theinductor coil, it might cause a serious accident in case an operatorwere to attempt to stir the molten material with a metal stirrer, anddamage to the inductor coil might also result by reason of ashort-circuit if two or more turns of the coil were engaged by themolten metal.

Referring to Figs. 1 and 2 of the drawings, a furnace structure 11includes an outer casing 12 which may be. of metal and is shown as ofsubstantially pot shape, the particular furnace which we illustratebeing one of the smaller sizes of such furnaces.

A Crucible 13 of any suitable refractory material is located within theouter casing 12 and is spaced therefrom and supported therein bygranular electric-insulating material 14, such as some form of zirconiumsand'or its equivalent, as usually employed in this art.

An annular plate 16 may be provided to cover the granular material 14 atthe top of the casing 12 where it is not covered by a pouring spout 17constituting a part of the Crucible 13.

It is to be understood that any suitable or Idesired means may besupplied to permit of tilting the furnace to pour' the molten metal andthat a cover for the furnace may be provided, but, as these details formno part of our present invention, we have not illustrated them.

An inductor coil 18 is located between the Crucible 13 and the casing12. The conductor constituting the plurality of turns of electricconducting material may be of any suitable or desired shape and is hereshown as being substantially rectangular in lateral section, this beingshown for purposes of illustration but it is to'be understood thatanysuitable or'desired shape of conductor,

method of support and insulation between adjacent turns, may beemployed.

A two-part protecting shield is located be tween the coil and thecrucible and, in the modification shown in Figs. l and 2, this shieldincludes a divided or laminated inner cage 21 and a substantiallysimilar laminated outer cage 22, each of substantially cylindrical shapeand so divided or slotted as to provide no closed electric circuit orcircuits therein which might be of such area or section as to causethegeneration of excessive amounts of heat therein by inductive ellects.

The two parts of the shield are insulated from each other by a tubularmember 23 which may be of mica, and the outer part 22 is located closelyadjacent to and within the inductor coil 18 and is spaced and insulatedtherefrom by a tubular member 24 which may also be of mica.'

The inductor coil is energized from a suitable source of electric energyindicated by inductors L1 and L2. A source of electric energy, includingsupply-circuit conductors 25 and 26, is connected to the two parts ofthe shield hereinbefore described, and a circuit controlling device 27,such as an electromagnetic circuit breaker` is provided in the circuitof inductor coil 18 and controlled by the owof current from thesupply-circuit conductors 25 and 26 and between the two parts of theshield.l For this purpose, stationary cooperating contact members 28,oi' the usual kind, may be connected in circuit with conductor L1, andan actuating coil 29' may be connected in circuitwith supply-circuitconductor 25 to, actuate a contact-bridging member-31 so that, in case acurrent of a predetermined value traverses supply-cir cuit conductors 25and 26 and coil 29, the supply of energy to inductor coil 18 isinterrupted.

The circuit breaker may be provided with means for controlling an alarm,including an auxiliary contact-bridging member 32 cooperating withstationary contact members 33 to control the energization oan alarm de-lvice 34, which may be visual or audible, from a source of electricenergy 36.

Referring more particularly to Figs. 3 and i of the drawings, we have'there 'illustrated a modied form of shield. v The main difierence isthat, instead of the two parts of the shield being located in coaxial'but radially displaced relation relatively to each other, as shown inFigs. 1 and 2, the two parts are in the same circular plane, butalternate so that strips or bars 37 ofone part of the shield willalternate in peripheral position with strips or bars 38 of the otherpart of the shield.

Suitable electrical connections are pro-- suitable mechanical means forholding they asomar er-actuating coil 29 is connected in this cir- Vcuit to be effective for the same purpose as that hereinbeforedescribed.

.In Figs'. 1 and 2, we have shown a ground connection 43 as beingprovided for the inner part ofthe shield and it may be desirable to usethis ground although this is not absolutely necessary when using atwo-part shield energized from a separate source of electric energy. y

As was hereinbefore stated, hair cracks may occur in the wall of acrucible, and molten material may escape through themI and into thegranular electric insulating material 14 and thus cause caking of thesame, and it is obvious that it is not always possible tov visuallyobserve such leakage of material in case of a completely enclosedfurnace structure. Hence, it may happen, if no protective device isprovided, that either the full potential of the circuit connected to theinductor coil may be effective at the molten material or at the Crucibleof electric-conductive ma- If molten material does escape through the lwall of the furnace and engages only a portion of the inner part of theshield, it will i,

eventually destroy the insulation between the two parts of the shieldand electrically connect them. rlhis permits a current to flow betweenthe two parts 21 and 22 of the shield and, if the effective currentvalue is large enough, it will eect deenergization of the inductor coil18, thereby not only calling attention, in an unmistakable manner, tothe dangerous condition of certain parts of the furnace, but alsoremoving the danger to an operator.

The device embodying our invention thus provides relatively simple meansfor electing interruption of the supply of energy to the inductor coilin case of breakdown of the insulation between the two-parts of theshields, as well as means for preventing energization of thecoil in caseof the breakdown parts. The device embodying our invention thus providesalso means for indicating the electrical.v condition oit the furnacestructure and, more specifically, of a predeterinined thereof, as wellas simultaneensly indiill cating the mechanical condition of thecrucible.

Various modications may be made in the device and system embodying ourinvention without departing from the spirit and scope thereof, and wedesire, therefore, that only such limitations shall be placed thereonas,

are imposed by the prior art or are set forth in the appended claims.

1We claim as our invention:

l. In an induction furnace having a crucible and an inductoi coilsurrounding it, a two-part shield located between the coil and theCrucible, electric-insulatingmaterial between the two parts of theshield, a source of electric energy lconnected to the two parts of theshield, .and electric means actuated by the breakdown of theelectric-insulating material between the two parts 'of the shield foreifecting interruption of the energizing circuit of the coil.

2. Iii an induction furnace having a crucible, an inductor coilsurrounding it, a twopart shield located between the coil and thecrucible, electric-insulating material between the crucible, the partsof the shield and the coil, and electric means for preventingenergization of the coil in case of electrical connection of the twoparts of the shield.

3. In an induction furnace having a crucible, an inductor coilsurrounding it, a source of electric energy connected to said coil, acircuit breaker in the circuit of said coil, a two-part grounded shieldbetween the coil and the crucible and electric-insulating materialbetween the coil and 'the crucible and between the two parts of theshield, electric in'eans operatively associated with the grounded shieldfor controlling'the energiza-r tion of the coil through said circuitbreaker in accordance' with 'the electrical 4condition of the insulatingmaterial between the two parts of the shield.

4.-. In an induction furnace having a crucilile, an inductor coilsurrounding it, a twopart shield between the coil and the crucible andelectric-insulating material between the o -1 l' r coil, the Crucibleand the two parts or the shield, electric means operatively associated iwith the shield and the coil to control the en 6. In an inductionfurnace having a crucible, an energizing coil surrounding it, two--partshield between the coil and the Crucible,

electric-insulating material between the coil, the crucible and the twoparts of the shield, a source of electric'energy connected to the twoparts of the shield, and electric means in the circuit of the two-partvshield for controlling tlie energization of the energizing coil inaccordance with the amount of current flowing between the two parts ofthe shield.

7. In an induction furnace having a crucible, an energizing coilsurrounding it, a twopart shield between the coil and the crucible andelectric-insulating material betweenfthe coil, the Crucible and the twoparts of the shield, electric means operatively associated with theshield and the coil to control the energizatioii of the coil inaccordance with the condition of the electric-insulatin material betweenthe two parts of the s ield,

engagement of the two parts of the shield ,i

by molten metal from the Crucible.,

9., In an induction furnace having a crucible, an energized inductorcoil surrounding it a two-ioart electric-conductin shield be.

'tween-the coil and the crucible and a source of electric energyconnected to the two parts u of the shield, means electrically connectedto the two-part shield and the inductor coil to effect deeiiergizationof the coil when elec tric current of a predetermined value iowa fromone part of the shield to the other part thereof.,

l0, in

an electric heating device having a heating coil in operative relationinatef,

rial to be heated, a multipart shield between the heating coil and thematerial being heated and sources of electric energy' connected to theheating coil and to the parts of the shield to energize the same, meanselectrically conf l 'to the heating coil and to the shield.

deenergizatioii of the heating coil w of an electric current ofpredetervalue between the n l l an electric heating neomei insulatingmaterial normally insulating the heating coil, the material being heatedand the parts of the shield from one another, electric means connected,in circuit with the mul- 5 ti-part shield and the heatin coil forcontrolling the energization' of t e heating coil in accordance with thecondition of the insulating material between parts of the shield.

In testimony whereof, We have hereunto 10 subscribed our names this 26thday of February, 1930.

JOHN V. BREISKY. THOMAS H. LONG

